This invention relates to a carton for packaging articles such as beverage cans, bottles, bricks and the like and more particularly to a slide type lock or panel-interlocking means for interconnecting two panels for forming a carton wall.
Slide type locks or slide-type panel-interlocking means have been well known in the field of package-manufacturing industry. A slide type lock comprises a tab and a slit. The tab is formed, for example, on an edge of a carton panel while the slit is defined in another panel. The tab is inserted into the slit and locked in the slit to interconnect the two carton panels. For slide locks to become reliable, it is essential that the tab and the slit be arranged to prevent undesired disengagement from each other. One of the conventional approaches for preventing the disengagement is to provide a crank-shaped section at each end of the slit and an outwardly projecting ear at each side edge of the tab. When inserted into such a slit, the tab is engaged at its ears with the carton material adjacent to the crank-shaped sections, which effectively prevents disengagement of the tab from the slit. Examples of the cartons taking such an approach are disclosed in U.S. Pat. Nos. 1,333,102; 3,064,877; 3,186,545; 3,305,161; 3,341,908; and 3,655,117, U.S. Design Patent No. 229,485, and French Patent No. 1,424,536, which are hereby incorporated by reference.
A drawback of the cartons using the above approach is that the material around the crank-shaped sections lacks structural flexibility, which not only interferes with smooth insertion of the tab but also causes the slit to remain slightly opened when the material is deformed due to the insertion of the tab. If remaining deformed after the insertion of the tab, the material around the crank-shaped sections is unlikely to function to prevent disengagement of the tab.
What is needed, therefore, is a carton having a slide-type lock wherein the tab insertion is facilitated and the tab-and-slit engagement is highly reliable to maintain the integrity of the carton.
According to the invention in one form, a carton having an improved slide-type lock is provided. The carton comprises first and second panels in an overlapping relationship, and an interlocking means for interconnecting the first and second panels. The interlocking means comprises a slit formed in the first panel, and a tab projecting from the free end edge of the second panel and received in the slit. The slit includes a main slit portion disposed generally along the free end edge of the first panel, an intermediate slit potion emanating from an end of the main slit portion and extending away from the free end edge of the first panel, and a terminal slit portion emanating from the intermediate slit portion and extending away from the main slit portion to be disposed generally along the free end edge of the first panel. The tab comprises an ear protruding from at least one of the opposite side edges of the tab. The carton is characterised in that a fold line is provided between the intermediate and terminal slit portions such that an engaging flap is defined by the fold line and the intermediate and terminal slit portions and connected to the first panel along the fold line. The carton is also characterised in that the ear of the tab is disposed in engagement with the engaging flap.
The above arrangement is of utility because when the tab is being inserted into the slit, the engaging flap is easily thrust aside by the tab due to the fold line. This facilitates insertion of the tab into the slit. The arrangement is further of utility because when the tab is fully inserted, the flap having been cleared by the tab is allowed to easily recover from the folded position because of the flexibility provided by the fold line. Without the fold line, the folded material tends to remain folded and hardly returns by itself to the initial unfolded position. The flap having returned to the unfolded position is ready to engage the ear of the tab to serve as a stopper for preventing the tab from coming out of the slit.
In a preferred form of the invention, the slit may further include an expansion slit portion emanating from the terminal slit portion and extending away from the free end edge of the first panel. The expansion slit portion serves to expand the end area of the slit when the first panel is manipulated to open the slit to facilitate insertion of the tab.
In another preferred form of the invention, the ear of the tab may be disposed adjacent to the free end edge of the second panel with a space therebetween so that the ear is provided with an edge defined for engagement with the engaging flap. This further insures that the engaging flap serve as the stopper.
In another preferred form of the invention, the first panel may include a panel body and a foldable panel portion connected to the panel body along a fold line, and the main slit portion may be formed in the foldable panel portion. In this form of the invention, it is further preferred that the intermediate slit portion is formed also in the foldable panel portion while the terminal slit portion is disposed in general alignment with the fold line between the panel body and the foldable panel portion. Such an arrangement allows the slit to wide open when the foldable panel is folded with respect to the panel body.